Polyolefins (POs) have many desirable properties, e.g. light weight, durability, low cost, etc., that make them attractive materials of construction for many consumer goods, e.g. interior and exterior automotive parts, decorative fascia for household appliances, and the like. However because of their nonpolar nature, POs do not readily accept paint, primers or decorative print. Most paints, primers and inks are polar in nature, and thus require a surface with some degree of polarity before they can adhere to the surface with any degree of desirable fastness.
Various techniques have been developed to address this problem. One typical and effective technique is applying a primer to the PO. Primer materials are typically compositions containing a maleated and/or halogenated polyolefin and an aromatic or water solvent and while widely recognized as effective, primers are expensive and their application is an extra step in the finishing of the PO article.
Another effective technique is to subject the surface of a PO article to a physical or chemical treatment, such as etching with a chemical abrasive, or irradiating with plasma, or exposing to a corona or flame. While generally effective, these methods are more complex in nature than the application of a primer, and thus more difficult to control in terms of quality and consistency from part to part.
Another technique is to modify the physical and/or chemical properties of the PO either by blending it with other polymers, or by incorporating into it one or more polar groups, or both. For example, U.S. Pat. No. 4,946,896 to Mitsuno, et al. teaches a paintable PO comprising 20-80 wt % (wt %) polypropylene; 5-38 wt % of an ethylene copolymer consisting of ethylene, an ester unit of either alkyl acrylate or methacrylate, and an unsaturated dicarboxylic acid anhydride; and 5-70 wt % ethylene-propylene rubber. U.S. Pat. No. 4,888,391 to Domine, et al. teaches a paintable polyolefin composition comprising a blend of a polyolefin as the continuous phase with an ethylene/acrylate/acrylic acid terpolymer as the discontinuous phase. U.S. Pat. No. 4,945,005 to Aleckner, Jr., et al. teaches paintable POs comprising 2-25 wt % of a copolymer of an ethylenically unsaturated carboxylic acid and ethylene; 3-50 wt % of an ethylene α-olefin copolymer; optionally a crystalline homopolymer or copolymer of propylene; 5-50 wt % of inorganic filler; and 10-35 wt % of a polyethylene or a copolymer of ethylene and α-olefin. EP 0 643 742 A1 teaches a paintable polyethylene comprising at least 50 wt % polyethylene grafted with at least about 0.01 wt %, based on the weight of the polyethylene, of an unsaturated organic compound containing at least one double bond and at least one functional acid group, e.g. maleic anhydride (MAH), and at least one thermoplastic polymer containing polar groups, e.g. polyurethane. U.S. Pat. No. 5,346,963 teaches that substantially linear ethylene polymers grafted with one or more unsaturated organic compounds containing ethylenic unsaturation and a carbonyl group, e.g., MAH, exhibit desirable compatibility and impact properties to various thermoplastic polymer blends. U.S. Pat. No. 5,424,362 teaches a paintable, thermoplastic composition comprising (i) 30-70 wt % of at least one polypropylene or graft-modified polypropylene, (ii) 0-40 wt % of at least one of a non-grafted substantially linear ethylene polymer and a graft-modified substantially linear ethylene polymer, and (iii) 0-50 wt % of an interpolymer of ethylene and an α,β-unsaturated carbonyl with the proviso that the sum of components (i) and (ii) is between about 30-70 wt %.
International Publication No. 2007/033117 relates to ethylene/α-olefin compositions containing at least one ethylene/α-olefin random interpolymer and at least one polydiene diol-based polyurethane, and where the at least one ethylene/α-olefin interpolymer has a PRR from −6 to 75, and a density less than, or equal to, 0.93 g/cc.
Beyond paintability and printability, POs do not adhere well to polar substrates such as polyamide, polyurethane, polycarbonate, acrylonitrile-butadiene-styrene (ABS) and blends of two or more of these materials. This is an important consideration in over-molding and high frequency (HF) welding applications. One response to this adhesion-failure problem has been blending the PO with a zeolite or a polar polymer, e.g., a MAH-grafted polymer or an ethylacrylate polymer.
While these and other modified PO compositions all demonstrate some degree of efficacy, a continuing interest exists in identifying and developing new paintable POs.